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From: Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>
Newsgroups: sci.electronics.design
Subject: Re: heating a cap
Date: Fri, 4 Oct 2024 16:24:30 -0000 (UTC)
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john larkin <JL@gct.com> wrote:
> On Fri, 4 Oct 2024 07:09:26 -0700, John Robertson <jrr@flippers.com>
> wrote:
> 
>> On 2024-10-03 4:36 p.m., john larkin wrote:
>>> I got a small (under 1" long) aluminum electro cap, 220 uF 63v, and
>>> cranked up the voltage. It started drawing a bunch of current at 105
>>> volts, got hot, and folded back to 80 mA at 87v.
>>> 
>>> It got too hot to touch in a couple of minutes, after roughly 500
>>> joules. Freeze spray let it go back up to 100 volts or so.
>>> 
>>> None of that seemed to damage it, so an electrolytic cap sort of has a
>>> built-in MOV.
>>> 
>> 
>> Caps have vents...eventually the electrolyte with evaporate and outgas 
>> and you are left with a slug of aluminum foil.
>> 
>> I've seen many thousands of caps fail over the decades, you don't want 
>> to push them above 85c (even if rated at 105c) unless you like short 
>> lifetimes. Heck even caps that are never over 50c will dry out 
>> eventually - 20 to 30 years in many cases. Seals aren't perfect.
>> 
>> I assume SMD electrolytics are the same.
>> 
>> Let's not talk about stress testing tantalum caps - "Bang!".
>> 
>> John ;-#)#
> 
> The usual MnO2 tantalums actually detonate, and a bit of peak current
> will set them off.  The polymer tantalums don't detonate.
> 
> Is there a reason to use polymer tants? I like tantalums for their
> just-right ESR for some voltage regulators, and I think the polymer
> tants are lower.
> 
> If you want low ESR, may as well use a polymer aluminum.
> 
> 

Some alpos are hybrid, i.e. they have water as well as polymer. I don’t
think they make hybrid polymer tants. 

Cheers 

Phil Hobbs 

-- 
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics